Factors affecting persistency and residual activity of herbicides in soil

本研究旨在获得影响除草剂在土壤中的持久性和残留植物毒活性的因素的基本信息，为制定合理的除草剂除草管理提供依据。研究结果表明：1.施药后土壤固相中的除草剂用量远大于土壤水中的除草剂用量，土壤水中的除草剂用量随施药时间的延长而显著降低。各除草剂在土壤固体中的含量因土壤类型不同而不同，但对土壤有机质的吸附量相似。结果表明，土壤有机质是影响除草剂在土壤中吸附的主要因素。2.除草剂的药效与土壤水中的浓度呈正相关，与土壤中的浓度无相关性，但与其活性成分(NOP)--萘丙胺除外。萘丙胺对土壤的药害作用取决于土壤水中NOP的浓度。土壤类型不同，残留的植物毒性活性不同，但其程度与土壤水中的浓度一致。3.除草隆和三氯乙烯对黑麦草幼苗生长的毒害作用是由土壤表层形成的除草剂处理层中的土壤水分吸收部分所诱导的，这说明除草剂或其活性代谢产物在土壤中的浓度是影响除草剂在土壤中的药效的主要因素，土壤水中除草剂的浓度是由土壤对除草剂行为的吸附和降解活性等因素以时间依赖的方式决定的。此外，目标杂草的出苗深度和对除草剂的吸收部位可能是决定土壤植物毒力的一个因素。

The study was conducted to obtain the basic information on factors affecting the persistency and the residual phytotoxic activity of herbicide in soil for developing the rational weed management by herbicides. The results obtained in the study are summarized as follows.1.The amount of any herbicide applied to soil was detected much greater in solid phase than in soil water at the application and the amount in soil water decreased more remarkably than in soil solid with time after application. The amount of each herbicide in soil solid was different between soil types but the amount of adsorption on soil organic matter was similar. The results demonstrated that soil organic matter was a main factor dominating the adsorption of herbicide in soil. 2.The phytotoxic activity of each herbicide was correlated with the concentration in soil water but not with the amount in total soil, except for naproanilide which was hydrolyzed to be its active compound (NOP). In case of naproanide application to soil, the phytotoxicity depended on NOP concentration in soil water. The residual phytotoxic activity differed in the soil types but the degree of phytotoxic activity was coincided with the concentration in soil water. 3.The phytotoxic activity of cumyluron and thenylchlor on the growth of Eleocharis kuroguwai or barnyaydgrass seedlings was induced by absorption of this herbicide by the absorptive parts from the soil water in the herbicide treated layer formed in the top-soil, regardless of emerging depth.These results suggest that the concentration of herbicide or its active metabolite is dominating factor for the phytotoxic activity of herbicide in soil and that the concentration in soil water is determined by soil factors such as adsorption and degradation activity on herbicide behavior in a time dependent manner. In addition, emergence depth and the herbicide-absorption parts of target weeds is suggested to be a factor determining the phytotoxic activity in soil.